Oxidation of ruthenium hydrides (η5-C5H4R)Ru(PPh3)2H (R=H, tBu, CH2Ph, CTol3). X-ray crystal structure determination of (η5-C5H4(CTol3))Ru(PPh 3)2H and an electrochemical study of its stable cation radical

Article abstract of DOI:10.1016/s0020-1693(97)05467-4

The oxidation of a series of cyclopentadienylruthenium hydrides (η⁵-C₅H₄R)Ru(PPh₃)₂H (R=H, tBu, CH₂Ph, CTol₃, CPh₂(p-MeOC₆H₄)) has been investigated by cyclic voltammetry. For R=H, tBu and CH₂Ph, uncomplicated reversible oxidation processes are observed. For the trityl-substituted species (R=CTol₃, CPh₂(p-MeOC₆H₄)), the cyclic voltammograms indicate the presence of two isomeric cation radicals that exist in a dynamic equilibrium. It is suggested that this may be the result of an interaction between the 17-electron Ru center in the cation radical and the π system in one aromatic ring to yield a weakly bonded 19-electron adduct of the cation radical. The first ESR spectroscopic data for a 17-electron cyclopentadienylruthenium hydride cation radical are reported for (η⁵-C₅H₄(CTol₃))Ru(PPh ₃)₂H⁺. The anisotropic ESR spectra showed no hyperfine structure. The X-ray crystal structure of the neutral hydride (η⁵-C₅H₄(CTol₃))Ru(PPh ₃)₂H reveals a sterically crowded molecule in which the trityl group eclipses the hydride ligand. Two tolyl groups on the CTol₃ ring substituent are on the same side of the Cp ring plane as the metal and induce steric repulsions in the molecule. Crystal data for (η⁵-C₅H₄(CTol₃))Ru(PPh ₃)₂H: space group P-1, a=11.3505(3), b=14.3263(3), c=17.3172(4) A?, α=102.005(1), β=98.348(1), γ=112.321(1)°, T=170 K, R₁ (F>4σ(F))=0.067, wR₂(1>2σ(1))=0.128.